1. Field of the Invention
The present invention pertains to piezoelectric resonators with extreme sensitivity to external pressure stresses, including a piezoelectric crystal made of a circular plate with at least one circle face, first and second electrodes each operating with one face of the crystal and means of holding the vibrating part of the crystal, applied to the edge of the crystal itself.
2. State of the Prior Art
Various examples of piezoelectric resonators of the abovementioned type are known.
According to one classical example, the resonator crystal is made of a circular plate of plane-convex or biconvex quartz, on the front faces of which metal electrodes, called adherent electrodes, are deposited directly.
According to another example of construction, the quartz plate with adherent electrodes surrounded by a quartz crown that acts as a support for the resonator crystal.
According to another example of construction, the resonator crystal is connected to a quartz crown by bridges cut in the crystal itself. The electrodes can be adherent or non-adherent and, in the latter case, the electrodes are deposited on quartz plates cut at the same angle as the crystal and the similar shape, and only the crowns of the electrode support plates are in contact with the vibrating crystal crown.
In these various examples of resonators, it is generally attempted to minimize the effect of all of the external pressures exerted on the resonator crystal, to create a time base offering a very stable frequency.
For resonator applications in the field of hydrostatic pressure transducers, on the other hand, it is desirable to increase the sensitivity of the resonator to external pressure stresses.
In one case or in the other the existing systems do not allow simple construction of a resonator with optimum sensitivity to external pressure forces.